Conventionally, a plurality of injectors is attached to a delivery pipe provided in an engine. During operation of the engine, fuel is repeatedly injected from those injectors. At that time, in the delivery pipe, fuel pressure pulsates by injection of each injector and thus different pressure pulsations resonate, or vibrate sympathetically. This may cause larger pulsation and variation of the fuel pressure. When the pulsation of fuel pressure becomes large in this way, a fuel injection amount from each injector may vary due to such large pressure pulsation. The control of air-fuel ratio of the engine becomes unstable, leading to deterioration of engine performance, stop of the engine, and generation of noise.
To restrain the pulsation of fuel pressure in the delivery pipe, accordingly, JP 8(1996)-270523A discloses a metal delivery pipe provided with a pulsation damper. In this case, however, the addition of the pulsation damper results in an increase in size of the delivery pipe and in the number of components.
JP 11(1999)-37380A therefore discloses a delivery pipe capable of reducing the pulsation of fuel pressure without adding a pulsation damper. This delivery pipe is molded of resin to have a capacity of 100 (cm3) or more and a shape of cross section including a straight part and a curved part. When viewed in three dimensions, the straight part forms a flat plate portion extending in a longitudinal direction of the delivery pipe and having flexibility and the curved part forms a curved plate portion extending in the longitudinal direction. This delivery pipe can absorb the pulsation of fuel pressure by use of flexibility of the straight part (the flat plate portion), thereby reducing the pulsation.